The bearing, as we can see in daily life, possesses clearance among their parts which seriously affects the precision of the overall assembly when it applies to assembling machines with relatively high precision; therefore, in order to eliminate the clearance inside the bearing, a prestressed force is applied on the bearing. But the rigidity of the bearing will vary under different prestressed forces. In general, the rigidity is higher when the prestressed force is large and lower when the prestressed force is small. Generally, heavy prestressed force is used for machines with high loading and light prestressed force is used on the bearing for machines with low loading.
What is more, the rotational speed is a very important factor to a bearing. The higher the rotational speed is, the lower usage life it is. Particularly, for the machine designed at high speed and also with high prestressed force, it is apt to result in suddenly dropping of bearing life. Therefore, the prior art's design, in most part, employs light prestressed force when it comes to bearing application at high speed.
As we can see in general application, for some machine assemblies, like the spindle of machine tool, the range of rotational speed is very wide, anywhere from tens of rpm to thousands of rpm and even up to tens of thousands of rpm. All of these are possibly the required speed range. In this situation, if we choose the light prestressed force and alleviate the problem of lower life at high speed, it will end up with the fact that the whole mechanism cannot sustain relatively heavier load at low speed. The inventors, therefore, in order to overcome the limitation of these applications at both high and low speed, perform testing in all respects and finally result in the design of present invention through countless trials and errors and have made it possible that a bearing has light prestressed force at high speed and heavy prestressed force at low speed.